1. Field of the Invention
This invention relates to polyamines and methods of using them for treating scale in various industrial process streams. Preferred embodiments relate to hydrophobically modified Si-containing polyamines that have been found to be particularly useful for treating aluminosilicate scale in difficult-to-treat industrial process streams, such as in the Bayer alumina process, nuclear waste streams and kraft paper mill effluent streams.
2. Description of the Related Art
The formation of scale is a problem in a number of industrial process streams. Scale is a solid material that generally forms on the surfaces of equipment that are exposed to aqueous process streams. Scale typically contains inorganic materials having relatively low aqueous solubility, including for example various hydrated sodium aluminosilicate materials such as amorphous aluminosilicates (e.g., aluminosilicate hydrogel), zeolites, sodalites and canerinites. The removal of scale by mechanical methods, e.g., by scraping, is often undesirable because such procedures may involve considerable expense in terms of process downtime, and may be impractical where the scale forms on surfaces of the process equipment that are difficult to access.
A number of chemical treatments have been developed to remove scale and/or inhibit the formation of scale in various industrial process streams. Such chemical treatments are generally applied by intermixing the treatment chemical with the process stream, thus allowing treatment of surfaces that are difficult to access and reducing or eliminating downtime. A number of Si-containing polymers have been developed in recent years and applied to the treatment of scale. See, e.g., U.S. Pat. No. 6,814,873; U.S. patent Publication Nos. 2005/0010008, 2004/0162406, 2006/0124553, 2004/0162406, 2004/0011744, and 2005/0274926; and WO 2004 009606 The foregoing patent publications are hereby incorporated by reference in their entireties, and particularly for the purpose of describing various types of scale, as well as particular Si-containing polymers and their use as anti-scalants in certain industrial process streams:
The Si-containing polymer and methods of using them described above represent a significant advance in the art, but have not completely solved the problem of scale formation in industrial process streams. Difficult-to-treat industrial process streams are particularly vexing. For example, there is a long-felt need for chemical treatments and methods of reducing and/or inhibiting scale in process streams that contain a relatively high level of sulfate, finely dispersed iron oxide (e.g., “red mud”), finely dispersed sodalite, and/or combined nitrate/nitrite.
A variety of Si-containing polymers have been developed for other purposes, but without any particular motivation to apply such non-analogous art to the treatment of scale. See, e.g., U.S. Pat. Nos. 3,560,543; 5,354,829; 6,262,216; 6,410,675; 6,429,275; 6,486,287; and 6,743,882; U.S. Patent Publication No. 2006/0159975; Canadian CA 2,193,155; Yang et al, Prepr. Pap.-Am. Chem. Soc., Div Fuel Chem 2004, 49(2), 599-600; and Macromol. Symp. 2004, 210, 329